Radio Frequency Identification (RFID) systems have become increasingly prevalent over the years. These systems can be used to identify people as well as objects. Typically, the systems include at least one RFID reader that transmits and receives radio frequency (RF) signals from one or more RFID tags within a predefined range. The RFID tags tend to be compact packages that are attachable to an object and include a microchip that is in communication with an antenna. The microchip is typically an integrated circuit for storing and processing information, modulating and demodulating the RF signal, and performing other specialized functions. The antenna of the tag is used for receiving and transmitting the RF signal and is usually tuned to a particular frequency.
In some implementations, RFID systems have been deployed with temperature sensing devices to detect when the temperature of a product, such as a perishable food item, exceeds a desired temperature. Typically, these implementations require that the sensing device (e.g. a thermister) have a continuous power source to detect a temperature change which adds to the cost of implementations. In addition, some implementations require that the sensing device also be connected to a comparator circuit to determine how far above or below a reference voltage is further adding to the cost of implementations. Accordingly, there is a need for an improved RFID system that can detect temperature change without use of a continuous power source or additional circuitry in a cost effective manner.